A slide member such as a slide bearing typically used in internal combustion engines for automobiles, etc. are formed by coating bearing alloy layer comprising Cu-based bearing alloy or Al-based bearing alloy over a back metal layer made of a steel sheet. Slide bearings generally have an overlay coated on the bearing alloy layer over an intermediate layer for improving their conformability with the mating elements, which is typically a shaft. The intermediate layer functions as a bonding layer to facilitate the bonding of the overlay with the bearing alloy layer. Overlays have been conventionally composed of soft Pb-based alloy and in some cases, Sn-based alloy.
Use of Pb is preferably avoided, because of the wide spread notion of Pb as a pollutant. Through research, Bi has been proposed as a possible alternative to Pb. Bi, however, is hard and thus, lacks in conformability. In order to overcome such shortcoming, JP H11-50296 A discloses a Bi-based overlay with one or more additive element(s) selected from Sn and In.
When the overlay is composed of Bi or Bi-based alloy, the intermediate layer is, at times, composed of Ag or Ag-based alloy.
When such configured slide bearings are subjected to high temperature in actual use, the additive elements within the overlay occasionally diffuse into the intermediate layer to disadvantageously reduce the conformability of the overlay.